The present invention relates to an aspheric mirror, a projection-type image displaying apparatus and a method of producing a projection-type image displaying apparatus.
An aspheric mirror having an aspheric reflective surface has been used for a variety of optical equipment. It has also recently been used for projection-type image displaying apparatuses enabling displaying of large images, such as, a front projector and a rear-projection TV.
The Un-examined Japanese Patent Publication No. 2006-18083 discloses a rear-projection-type image displaying apparatus having an aspheric mirror. The Un-examined Japanese Patent Publication No. 2004-93944 discloses optical-axis adjustments for an aspheric mirror.
Projection-type image displaying apparatuses with an aspheric mirror have a displaying mechanism as follows: Light from a light source is emitted to an aspheric mirror, carrying an image, via an image displaying device, such as, a liquid crystal image displaying device. The image is reflected from a reflecting surface formed on the aspheric mirror and projected onto a screen, as a large image.
The reflecting surface formed on the aspheric mirror is a portion of an aspheric shape symmetrical with respect to an optical axis. The location and orientation of the optical axis are thus difficult to find out from its shape. The aspheric mirror is required to be precisely mounted on a specific location given in design along an optical path and with respect to an optical block that emits light.
An image projected onto a screen is more distorted or has more non-uniform resolution as the location at which the aspheric mirror is actually mounted is more deviated from the location given in design, thus suffering from lowered quality. This is more remarkable for a larger screen on which images are enlarged at a larger scale.
There is thus a demand for higher accuracy in installation of the aspheric mirror.
Disclosed in Un-examined Japanese Patent Publication No. 2006-18083 is installation of an aspheric mirror in a rear-projection-type image displaying apparatus in accordance with a positional relationship between support members and attachments fixed at the side faces of the aspheric mirror and the corresponding parts at the apparatus' side.
In this scheme, however, the aspheric mirror is not installed in the displaying apparatus with no direct respect to the location and orientation of the optical axis of the mirror. It is difficult to accurately place the reflecting surface of the mirror at a desired location and at a desired angle due to deformation of the mirror, variation in size of support members and attachments, etc., and inconsistency in assembly, resulting in distortion or non-uniform resolution of images on a screen.
The installation scheme also causes variation in location of the aspheric mirror in mass-production of rear-projection-type image displaying apparatuses. Even a slight variation of the mirror location in each apparatus could cause quality gap among the apparatuses.
Disclosed in Un-examined Japanese Patent Publication No. 2004-93944 is optical-axis adjustments for an aspheric mirror with analysis of images reflected from the mirror mounted on a stage rotating by a small angle while parallel beams are emitted to the mirror. It is difficult to adopt such complex adjustments and analysis to optical-axis adjustments for aspheric mirrors in projection-type image displaying apparatuses.